Electric metal vapor lighting tube



Oct. 5, 1937. M. PlRANl ET AL ELECTRIC METAL VAPOR LIGHTING TUBE Filed March 11, 1936 Fig.2

y f e mlwm hi e o 25 ,w b 0A nlm ee ew fl a .mwa h MM T Patented Oct. 5, 1937 PATENT j OFFICE 2,094,668 ELECTRIC LIETAL VAPOR LIGHTING TUBE Marcello Pirani and Martin Reger, Berlin, Germany, assignors to General Electric Company, a corporation of New York Application March 11, 1936, Serial No. 68,306 In Germany March 13, 1935 4 Claims.

Our invention relates to improvements in electrio metal vapor lighting tubes, and more particularly in tubes of the type containing rare gas and having its glowing electrodes heated by a battery or another source of electric energy. The objects of the improvements are, first, to provide a lighting tube of increased life, second to provide a tube in which the electron emission rapidly is brought to the intensity needed for causing the main or are discharge between the electrodes, and, third, to provide a tube in which the metal vapor deposited in service at some parts of the wall of the tube is revaporized so that the loss of metal vapor by condensation on cold parts of the tube is prevented. With these and other objects in view our invention consists in providing a plurality of glowing electrodes at either end of the tube, the said glowing electrodes located at each end of the tube being connected in shunt 29 and tea common heating circuit. I

For the purpose of explaining the invention several examples embodying the same have been shown in the accompanying drawing in which the same letters of reference have been used in all the views to indicate corresponding parts.

In said drawing Fig. 1 is a diagrammatic'al elevation showing a lighting tube and its electrical connection,

Fig. 2 is a sectional elevation on an enlarged scale showing the sets of electrodes located at one end of the tube, and

Fig. 3 is a similar sectional elevation showing a modification.

As shown in Fig. l the lighting tube comprises an elongated receptacle i made from glass and containing a. noble gas and a suitable metal such as sodium which is adapted to be vaporized at elevated temperature. The pinches 2 provided at the ends of the tube are formed with two nippics I having leading-in wires 3 sealed therein, the said leading-in wires being adapted to supply the heating current and also the discharge current. To the inner ends of the wires 3 two glowing electrodes 4 and 5 are connected inshunt, the 5 said electrodes being spaced from each other in the direction of the path of the electrons and the longitudinal axis of the tube. It will be understood that leading-in wires and electrodes are provided at either end of the tube as is shown 50 in-Fig. 1. The electrode 4 or 5 consists of a heating coil 8 having a rod 9 embedded therein, the said rod being made from or containing a substance adapted to emit electrons.

In the example shown in Fig. 1, the leading-in 55 wires 3 located at either end of the tube are vaporization within the tube.

located respectively in circuits l0, l0, including the secondary ll of a transformer the primary l2 of which is connected to the net l3 supplying alternating current say of 220 volts. One of the leading-in wires 3 located at either end of the 5 tube is connected by a lead It to the net l3 and one of the said leads it includes a choking coil it. As shown the circuit of the primary it of the transformer includes the choking coil l5.

In the operation of the tube the circuits there- 10 of are connected to the net 13, and thereby heating current is supplied to the electrodes 4 and 5 through the secondary H of the transformer. After the electrodes have been sufficiently heated electron emission takes place, and 5 therefore the current of the net is caused to flow through the beam of electrons emitted between the said electrodes. By reason of the comparatively high voltage drop at the. choking coil l5 the heating current now falls off sub- 20 stantially to half of its value so that heating of the electrodes by the transformer is practically interrupted.

We have iound,-that in our improved tube the arc discharge always takes place exclusively 25 from the glowing electrode t or 5 which has the higher electron emission, and where the glowing electrodes are alike in character the are discharge ordinarily takes place from the glowing electrode which is nearest to the path of the dls- 3 charge. When in service one of the glowing electrodes is broken or has been spoiled by continued consumption of the. active substance emitting electrons the arc discharge is automatically transmitted to another electrode which is still in work- 35 ing condition. It will be understood that thereby the life of the tube is considerably increased.

Further, when the tube is switched in the electron emission is rapidly brought to the intensity necessary for causing ignition of the main dis- 4O charge, for the reason that during the heating period all the electrodes emit electrons.

When the tube is first switched in the metal such as sodium is at first uniformly distributed by When however in service at first the electrodes 4 are operative and the electrodes 5 inoperative, the median parts of the tube located between the electrodes 4 are heated to higher temperature than the end portions of the tube located beyond the electrodes 4. Therefore the sodium vapor gradually migrates from the median part of the tube to the end parts thereof and it is condensed within the said end parts, so that gradually the active portion of the tube becomes poor in sodium vapor. When after some time of service the glowing electrodes 4 have been consumed the electrodes 5 are automatically made. operative, and the discharge is transmitted thereto by reason of the smaller cathode fall.

Now the glowing electrodes 5 heat the adjacentends of the tube with higher intensity than the median part of the tube and thereby the sodium which has been deposited within the end portion of the tube is again vaporized and it is transmitted to the median part of the tube. Where at the beginning of the operation of the tube at first the outer electrodes located near the ends thereof are made operative, the sodium located at the said ends gradually migrates towards the middle of the tube, and it is precipitated on the wall thereof. When after some time of service the inner electrodes 4 become operative the said sodium is again vaporized and transmitted to the .end parts of the tube. Which one of the electrodes 4 or 5 is first made operative depends on the dimension of the tube and the energy needed for emitting electrons from the said electrodes. When the causing electron emission is considerably larger in the electrode 4 than in the electrode 5, for example by reason of the character of the active oxide, the outer electrode 5 may first become operative andaccordingly regulate the transmission of the sodium vapor. This migration of the metal vapor does not result in the complete consumption of the vapor .at the said portions of the tube, but only in a reduction'of the metal vapor at the said parts of the tube.

It appears therefore that in our improved tube the correct pressure of the metal vapor is maintained which results in a good efficiency of the tube without providing an additional supply of metal within the tube, which frequently spoils the tube by deposition of metal on the wall thereof.

In many cases it may be desirable to determine beforehand which one of the two electrodes 4 or 5 connected in shunt is first to be operative, and for this reason it is preferred to provide a resistance in the circuit of one electrode or different resistances in both electrodes, or the glowing electrodes are made from difierent active materials, so that the energy needed for causing electron emission is different in both electrodes, and the sum of the fall of voltage in the leading-in wires and the cathode fall is smaller in one electrode than in the other one. For this purpose it is suflicient, for example, to provide a resistance 6 of a few ohms in one or both leading-in wires of the electrodes 4, 5, so that with the same emission energy only the resistance of the leading-in wire is varied. But we may also provide the electrodes 4 and 5 with active material of different character, so that there is only a difference of the cathode fall, or we may combine both expedients, by reducing the resistance of the leading-in wire of one of the electrodes and simultaneously providing the electrodes 4 and 5 with active coatings of different character.

We have found that good results are obtained if the life of the glowing electrode which is first made operative is such that it corresponds to the reduction of the light intensity caused by the conditions of the structure, the gaseous filling and the load of the tube. For example it may be made such that already with a reduction of the light intensity by 15% the electron emission is reduced so far that the discharge is automatically maintained or assisted by other means which are known in, the art.

The glowing electrodes may be continuously heated during the whole operation of the tube with the same or reduced voltage. But heating of the electrodes may also be interrupted after ignition by hand or automatically,

In the construction shown in Fig. 2 the electron emitting substance is provided by the rod 9. But we wish it to be understood that elecwhich the heating coil itself has a coating of active material. In Fig. 3 we have shown a modification in which the active material of the electrode is indirectly heated. As is shown in the said figure the electrode comprises a heating coil I 6, a tube I l of non-conductive material such as magnesia, a coating ll! of metal such as tungsten, and a coating I 9 of active material such as barium oxide.

We claim:

l. A gaseous electric discharge device comprising a container, electrodes sealed therein, a gaseous atmosphere therein, one of said electrodes comprising a plurality of individual thered at different distances from ,the opposite electrode, each of said thermionic elements being capable of supporting the discharge incident at said electrode. 2. A gaseous electric discharge device comprising a container, electrodes sealed therein, a gaseous atmosphere therein, one of said electrodes comprising a plurality of individual thermionic elements connected in-parallel between a common pair of current container, said thermionic elements being mounted at different distancesfrom the opposite electrode, each of said thermionic elements being capable of supporting the discharge incident at said electrode, and a resistance connected in series with one of said thermionic elements.

3. A gaseous electric discharge device comprising a container, electrodes sealed therein, a

leads sealed into said higher electron emissive capacity than the other of said elements.

4. A gaseous electric discharge device comprising a container, electrodes sealed therein, a gaseous atmosphere therein and a quantity of vaporlzable material therein the vapor of which is capable of emitting light, one of said electrodes comprising a plurality of individual thermionic elements connected in parallel between a common pair of current leads sealed into said container, said thermionic elements being mounted at different distances from. the opposite electrode,. each of said thermionic elements being capable of supporting the discharge incident at said electrode, the parts of said container extending beyond the discharge path between said electrodes being at a lower temperature than the other parts of said container during the operation of said device to cause deposits of the condensed vapor thereat, one of said thermionic elements being mounted adjacent said lower temperature container part.

MARCELLO PmANl.

L- TIN REGER. 

